The present invention concerns a process of construction of an internal combustion engine of a type containing at least one cylinder, comprising a work chamber of a volume which is able to vary by the travel of a piston in the cylinder between a high dead centre position and a low centre position under the action of forces of pressure, periodically generated in the said chamber, with each cylinder associated with a means of intake and evacuation of a gaseous fluid, the piston of each cylinder being connected to a crankshaft of the engine.
It also concerns an engine for the implementation of this process.
The majority of current engines work in a four-stroke thermodynamic cycle. At a first stroke called intake or suction, the piston retreats or descends in the cylinder which is filled with an air-fuel mixture (a classical petrol engine, that is to say, with ignition controlled according to the Otto cycle) During a second stroke, the piston rising in the cylinder compresses the said mixture and the fuel evaporates due to the rise in temperature in the cylinder. When the piston approaches its high dead centre, a spark is generated which detonates at the points of a sparking plug, ignites the gaseous mixture, bringing about combustion and an abrupt rise in temperature and pressure in the cylinder.
During a third stroke, in re-descending or retreating in the cylinder, the piston allows the gases of combustion to expand and it is at that moment that useful work is produced. When the piston approaches its low dead centre, the gases, which are still under a certain amount of pressure, escape through an exhaust valve located in the cylinder head. During a fourth stroke, the piston again rises and the said exhaust of the burnt gases is thus completed.
The distance traversed by the piston during the four strokes of this cycle is the same on each occasion, especially that which is traversed during the process of compression of the piston (second stroke) and that traversed during the process of expansion (third stroke). Thermodynamic considerations show that the higher the ratio of expansion, the greater the output of energy, that is to say, the higher is the ratio of useful work to the heat supply of the fuel. In a case where these two ratios, that of compression and that of expansion, are no longer joined and forced to be equal, the same considerations show that for a given fixed expansion ratio, the said energy output increases with a falling rate of compression.
Moreover, in order to reduce the weight and dimensions of internal combustion engines, as well as the friction generated inside the same, it is desirable to increase the power density of such engines. The said increase of the power density is obtained, in particular, by increasing the air intake into the cylinder by the same volume, by allowing an intake of pre-compressed air into the engine. In the case of a petrol engine, this pre-compression must be accompanied by a reduction in the rate of compression of the engine, in order to avoid the phenomenon of spark ping, that is to say, the spontaneous partial detonation of the air-fuel mixture, which, should it occur, would destroy the walls of the cylinder combustion chamber. The increase in power density of a classical four-stroke petrol engine must therefore be accompanied by a reduction in the rate of compression and consequently also in the rate of expansion, taking into account the mandatory equality of the two rates, which will ultimately decrease the output of energy.
In the case of an internal combustion engine which is able to withstand a high supercharge, the adjustment of the load or of the power of the engine shall largely be effected by the adjustment of the delivery pressure of the compressor in question and no longer, as in the case of a classical four-stroke spark ignition engine, by a throttle valve at the intake. The consequence of this is that the adjustment of the load of this engine by means of the delivery pressure of the compressor, makes it possible to avoid losses called xe2x80x9cby pumpingxe2x80x9d, which are met in the adjustment of the classical load via a throttle valve. In fact, throttling the natural suction generates a pressure in the cylinder during the intake stroke of the piston, a pressure which is lower than the environmental pressure. On the other hand, the counter-pressure during the exhaust stroke of the piston, even with a partial load, will always be in the neighbourhood of the environmental pressure, which will lead to a negative balance of mechanical work of the crankshaft throughout the intake and exhaust cycles.
The present invention has the principal object of increasing the energy output as well as the power density of an internal combustion engine, by the implementation of an electrodynamic cycle within a piston machine, which makes possible the decoupling of the compression ratio and the expansion ratio. The interest is in optimising, on the one hand, the expansion of the gases of combustion in such a way as to optimise the energy output and on the other hand, to reduce the compression ratio, in order to make possible a high supercharge of the engine in question, in order to increase its power density.
This object is achieved by the insertion of additional time into the four-stroke cycle of the engine, which will be the second expansion of the gases of combustion by means of an additional cylinder. The said cylinder will function, looked on separately, according to a two-stroke cycle that is to say that the piston of this cylinder, in retreating or descending in the cylinder, will on each occasion expand the gases of combustion for a second time (fourth stroke) and then, advancing in the said cylinder, it will evacuate these gases (fifth stroke). The five-stroke cycle of the engine according to the present invention will consist in the intake of air or an air-fuel mixture, its compression followed by combustion, the first expansion of the gases of combustion, their second expansion and finally the exhaust of the gases of combustion. The intake, the compression and the first expansion will take place in the same small cylinder called a high-pressure combustion cylinder. The compression ratio, as well as the first expansion ratio, will consequently be equal. The second expansion will be effected by two cylinders during the decantation of the gases of combustion from the small combustion cylinder, the piston of the latter travelling to its high dead centre, to the large low-pressure cylinder, the piston of the low-pressure cylinder travelling to its low dead centre. The overall expansion ratio will be the product of the volume ratio of the first expansion and the volume ratio of the second expansion. This overall expansion ratio will, in fact, be equal to the ratio of the low pressure piston swept volume, the low-pressure cylinder being in the low dead centre position, divided by the volume of the combustion chamber of the high-pressure combustion cylinder, the latter""s piston being in the high dead centre position.
Thus, the invention provides a process of construction of an internal combustion engine of a type comprising at least one cylinder, which includes a work chamber of a volume which can vary through the travel in the cylinder of a piston between a high dead centre position and a low dead centre position, under the action of pressure forces periodically generated in the said chamber, a means of intake and evacuation of a gaseous fluid being associated with each cylinder, the piston of each cylinder being connected to an engine crankshaft and which uses at least, on the one hand, a cylinder which functions as a low-pressure cylinder according to a two-stroke mode which comprises intake accompanied by expansion, generating useful work during each stroke of the piston of the low-pressure cylinder to its low dead centre and the exhaust of a gaseous fluid during each stroke of the said piston towards its high dead centre and on the other hand, two cylinders functioning as combustion cylinders in the four-stroke mode, comprising the intake of air or of an air-fuel mixture during the first stroke of the piston of each of the combustion cylinders to its low dead centre, the compression of this air or air-fuel mixture during the first stroke of the piston to its high dead centre, followed by combustion, the expansion of the gases of combustion during the second stroke of the piston to its low dead centre generating useful work and the delivery of the gases of combustion during the second stroke of the piston to its high dead centre, the piston swept volume of each of the combustion cylinders being lower than that of the low-pressure cylinder and the combustion cylinders delivering their gases of combustion in alternation to the low-pressure cylinder, with a view to a second expansion of the gases of combustion and their exhaust from the engine and comprising a means of excess feeding the combustion cylinders, the process being characterised by the fact that the volume compression ratio of the combustion cylinders is relatively low, so as to be able to be highly supercharged.
The invention also provides an internal combustion engine for implementing the aforementioned process, the internal combustion engine comprising five cylinders arranged in line, including three high-pressure combustion cylinders and two low-pressure cylinders, two combustion cylinders being located at the ends of the crankshaft to which are connected the pistons of the two cylinders, the third high-pressure combustion cylinder being located in the centre and able to communicate with the two adjacent low-pressure cylinders, respectively by means of a valve and a decanting manifold in such a way, as simultaneously to transfer, during the second expansion cycle, the gases of combustion contained in the central combustion cylinder and in the two low-pressure cylinders which are associated therewith, the said low-pressure cylinders receiving, during a revolution of the crankshaft occurring during the travel of the piston to its low dead centre, all the gases of combustion contained in the combustion cylinder located at the end of the crankshaft and next to the low-pressure cylinder in question.
According to yet another embodiment of the invention, the internal combustion engine comprises an odd number, greater than five, of cylinders arranged in line in such a way that at the ends of its crankshaft are located two high-pressure combustion cylinders and in such a way that the other high-pressure combustion cylinders are located between two low-pressure cylinders and are able to communicate with the two adjacent low-pressure cylinders, respectively by means of a valve and a decanting manifold, so as simultaneously to transfer, during the second expansion cycle, the gases of combustion contained in the combustion cylinder, to the two low-pressure cylinders which are associated therewith.
The engine moreover comprises a means of controlling the supercharge pressure of air or of the air-fuel mixture of the combustion cylinders, in order to effect an adjustment of the engine load for a given speed, largely of the range of the functioning torque thereof and a compressor driven mechanically or a turbo-compressor unit, whose turbine is driven by the additional expansion of the engine exhaust gases, in order to provide the pre-compression of air or the air-fuel mixture, cooled if necessary by means of a heat exchanger, the inlet of the turbine being connected to a collector of the gases of combustion, fitted with a valve of the waste gate type which makes it possible, when it is open or partially open, to divert all or a part of the gases of combustion directly to the engine exhaust.
The intake manifolds of the combustion cylinders comprise a means of introduction of the fuel into the pre-compressed fluid, such that the controlled means of injection or carburetters and the work chambers of the combustion cylinders, are each of them equipped with a means of igniting the air-fuel mixture.
The work chambers of the combustion cylinders comprise, according to the variant of the embodiment, a means of direct injection of the fuel into the compressed air to the end of the compression cycle in the cylinders in such a way that the fuel ignites spontaneously.
In a variant, the work chambers of the combustion cylinders comprise a means of direct injection of the fuel into the compressed air during the compression stroke in respect of the variable ratios of weight of air to the weight of fuel and which are controlled according to the engine load, the work chambers of the high-pressure combustion cylinders being equipped with a means making it possible to ignite the air-fuel mixture.
According to another variant, the low-pressure cylinder comprises exhaust ports fitted inside the former, which wholly or partially evacuate the gases of combustion contained in the cylinder and which are uncovered by the piston of the cylinder, when the latter is in a position close to its low dead centre.
In a case where the engine comprises of turbo-compressor unit which makes possible the pre-compression of the air or the air-fuel mixture at the intake of the combustion cylinders, there are provided, according to another variant, up to three different exhaust channels or exhaust manifolds which are fed in a non-simultaneous manner and which make it possible during the stroke of the low-pressure cylinder piston towards its high dead centre, to deliver the gases of combustion contained in the cylinder, in the direction of the inlet of the turbine, all the said exhaust manifolds except the last one comprising a deflection flap of the gases of combustion, controlled individually according to the engine load and which, when in an open position, leads the gases of combustion from the low-pressure cylinder directly to the exhaust and which, when closed, guides the gases of combustion into the collector of gases of combustion connected to the inlet of the turbine, the last exhaust manifold being the first in communication with the work chamber of the low-pressure cylinder.
Advantageously, each of the aforementioned decanting manifolds comprises an auxiliary decanting valve associated with the low-pressure cylinder head and which opens approximately synchronously with the principal decanting valve of the same decanting manifold being associated with the head of the combustion cylinder.